Motor powered operators for garage doors and the like are in wide use. Such systems generally work reliably and efficiently, however, they do raise the risk of injury or damage due to people or objects in the path of the closing door or gate. For this reason, it is common to fit safety means, which automatically monitor the resistance encountered by the moving closure (eg. by monitoring the speed of movement) and stop or reverse the travel if an unexpected resistance is encountered.
Further, a known safety measure is the inclusion of an infrared transmitter and receiver hard wired to the operator, positioned across the door opening and configured such that if an obstacle is detected between the transmitter and receiver, a signal is sent to the operator controller to stop or reverse the movement of the door. Generally, the transmitter and receiver are located near the bottom of the door tracks close to the ground. In some jurisdictions, the inclusion of such an obstacle detection device is required by the relevant regulations (such as those based on the UL Standard 325, which applies to residential garage door openers manufactured for sale in the United States).
Systems have been proposed in the past for wireless safety systems, such as that described in U.S. Pat. No. 5,493,812 to RMT Associates. A detection means, being an infrared transmitter/receiver system, having two states, a low power state (standby mode) insufficient to allow obstruction detection, and a high power state (operational mode) sufficient to allow obstruction detection. The system can switch from one state to the other in response to, for example, an acoustic or vibration signal transmitted over the garage door tracks, the signal indicating that the garage door is moving, and that the obstruction detection system must therefore switch into operation mode. When in operation mode, the door controller continuously monitors wireless approval signals sent from the obstruction detection system, until the door is open or closed or until an obstruction is detected.
One of the drawbacks of the system of U.S. Pat. No. 5,493,812 is that when in standby mode there is no communication at all between the obstruction detection system and the door controller. Audio frequency receivers continuously ‘listen out’ for the movement of the door in order to switch into operational mode. The use of an acoustic or vibration signal is prone to problems, as vibration or noise other than movement of the door may readily and frequently switch the obstruction detection system out of standby mode, thus defeating the objective of saving battery power. In addition, audio frequency monitoring in standby mode would use a significant amount of power. U.S. Pat. No. 5,493,812 mentions as a possible alternative the use of a radio frequency or infrared signal to wake up the obstruction detection system, but does not discuss how this may be accomplished. The document makes clear that such alternative methods are undesirable as they would require more energy in the dormant state, further contemplating that the audio/vibration detection approach may need to be partially self-powering, the frequency sensor being used to convert audio energy to electrical energy so to assist in powering the sensor.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date (a) part of common general knowledge, or (b) known to be relevant to an attempt to solve any problem with which this specification is concerned.